A “‘two-way radio’” is a radio that can both transmit and receive, e.g., a transceiver, unlike a broadcasting receiver which only receives content. Two-way radios are available in mobile radio, stationary or base station radio and hand-held portable configurations. Hand-held radios are often called walkie-talkies, and include “push-to-talk” or “press-to-transmit” buttons to activate the transmitter. These half-duplex communications devices generally are not configured to support simultaneous two-way communications. One or more mechanisms typically are implemented in half-duplex communications devices to help ensure that is in a transmit mode only at the appropriate times. A push-to-talk (PTT) button places the communications device in a transmit mode while pressed or engaged and returns the communications device to a receive mode when the PTT button is released or disengaged. A voice operated (VOX) feature provides that a user's voice or other sound triggers the communications device to enter a transmit mode.
The first truly mobile two-way radio was developed in Australia in 1923. In 1933, the Bayonne, N.J. police department successfully operated a two-way system between a central fixed station and radio transceivers installed in police cars. This allowed for rapidly directing police response in emergencies. During World War II, walkie talkies, or hand held transceivers were used extensively by air and ground troops.
Conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time. The proper channel is selected by a user. The user operates a channel selector or buttons on the radio control panel to pick the channel. In multi-channel systems, channels are used for separate purposes. A channel may be reserved for a specific function or for a geographic area. Motorola uses the term “mode” to refer to channels on some conventional two-way radio models. In this use, a mode consists of a radio frequency channel and all channel-dependent options such as selective calling.
The use of two-way radios significantly improved communications and therefore effectiveness of military actions during and after WWII. The SCR 300 is the two-way radio or walkie talkie used by US forces towards the end of war. The SCR 300 comprised a backpack unit and a handset connected to the backpack, and weighed 30-40 pounds. Motorola (Galvin Manufacturing) developed the first hand-held two-way radios shortly thereafter (SCR 536), were became available at the platoon and squad level.
Various handsets have developed for use with two-way radios for military applications, for example, H-207/VCR, H-189/GR, H-250. The H-189 handset is a rugged repairable handset unit molded out of polycarbonate lexan that utilizes a 1000 Ohm earphone element, a 150 Ohm dynamic noise cancelling microphone, a PTT switch and 6 foot retractile cord terminating in a 5-pin audio connector. The handset is configured to be interchangeable with H-250 Handset, and is intended for use with military man-pack radio equipment such as AN/PRC-70 and AN/PRC-77.
While such known radio handsets are quite effective for intended military applications, they are not without shortcomings. Such conventional radio handsets are physically cumbersome, and are constructed with limited operational electronics capabilities.